Heretofore, for example, a pipe joint has been widely adopted, which is fastened for enabling introduction and discharge of a fluid with respect to a fluid pressure device or the like, with a tube being connected to the pipe joint. In this case, a tapered female screw thread is formed in the fluid pressure device, whereas a tapered male screw thread adapted to the tapered female screw thread is engraved onto the pipe joint, and the tapered male screw thread is screw-inserted into the tapered female screw thread. As disclosed in Japanese Laid-Open Patent Publication No. 04-000085, the present applicants have already proposed a pipe joint, which includes and makes use of tapered screw threads in this manner.
Incidentally, generally, for assuring airtightness and liquid-tightness more securely, a sealing tape is wrapped around the male screw thread, or alternatively, a sealing material is coated thereon when the male screw thread is screw-engaged with the female screw thread.
A structure having this type of tapered screw threads is shown in FIG. 6. In FIG. 6, for example, reference numeral 2 indicates an end cap of a pneumatic cylinder. A tapered female screw thread 4 is engraved in the end cap 2. The tapered female screw thread 4 is a female screw thread with which a tapered male screw thread of a pipe joint according to Japanese Industrial Standards is screw-engaged.
Reference numeral 6 indicates a pipe joint, which is screw-engaged with the tapered female screw thread 4. The pipe joint 6 is made from a metallic material, and more specifically, includes a cylindrically shaped main body 8, a hexagonal fastening member 10, for example, for facilitating rotation of the pipe joint 6 using a wrench or the like when the main body 8 is screw-inserted into the tapered female screw thread 4, an o-ring 14 installed in an annular groove 12 provided on one end of the main body 8, a sharp projection 16 circumferentially disposed around the vicinity of the o-ring 14, and a tapered male screw thread 18 provided at the other end of the main body 8 and which is screw-inserted into the tapered female screw thread 4. Further, a penetrating passage 20 for introduction and discharge of a fluid is provided in the main body 8 extending along the axial direction of the main body 8.
To the pipe joint 6, which is constructed in the foregoing manner, a one-touch coupling 22 is connected. The one-touch coupling 22 includes a bent main body portion 24 made of a synthetic resin material, and a coupling portion 26, which is installed in one end of the main body portion 24. The coupling portion 26 is a conventional article made up from a chuck, a collet, a release bush, a seal ring, etc., and thus, detailed description of the coupling portion 26 is omitted.
For installing the pipe joint 6 into the tapered female screw thread 4 of the end cap 2, a sealing tape is wound around or alternatively a sealing material is coated beforehand onto the periphery of the tapered male screw thread 18. Additionally, a wrench is latched onto the fastening member 10 and the pipe joint 6 is rotated clockwise thereby. As a result, the pipe joint 6 is gradually screw-inserted into the tapered female screw thread 4, and as shown in FIG. 6, after the pipe joint 6 has been screw-inserted a predetermined distance, rotation of the fastening member 10 is stopped.
More specifically, with this type of tapered screw threads, a lower surface of the fastening member 10 does not come into abutment against a surface of the end cap 2, but rather, a state is observed in which the tapered male screw thread 18 remains exposed to the exterior. Such a condition complies with regulations according to Japanese Industrial Standards.
Next, the one-touch coupling 22 is mounted and latched in the pipe joint 6. More specifically, another end of the one-touch coupling 22 is inserted on the side of the o-ring 14 of the pipe joint 6. As a result, an engagement part made up from the sharp projection 16 bites into an inner wall part of the main body portion 24, which is made from a synthetic resin material, whereby the one-touch coupling 22 is connected integrally with the pipe joint 6 so that introduction and discharge of a fluid can be carried out.
To enable integrated attachment of the pipe joint 6 and the end cap 2, concerning the screw-engagement of the tapered male screw thread and the tapered female screw thread, according to Japanese Industrial Standards, for example, the tapered female screw thread 4 and the tapered male screw thread 18 must be of sufficient length. Consequently, even if the tapered male screw thread 18 is screw-inserted into the tapered female screw thread 4, the bottom end surface of the fastening member 10 cannot come into contact with the upper surface of the end cap 2, and a portion of the tapered male screw thread 18 remains exposed to the exterior.
Additionally, in actuality, it is difficult and troublesome to carry out a confirmation operation to ensure that the tapered male screw thread 18 has been fastened and fitted sufficiently with respect to the tapered female screw thread 4, so as to assure an airtight or liquid-tight state.
Furthermore, when an airtight or liquid-tight state is assured by wrapping a sealing tape around or coating a sealing material onto the tapered male screw thread 18, the number of assembly steps is increased, and costs for the sealing tape or sealing material lead to a rise in costs overall, which are reflected in the product price.
Still further, because the length of the tapered female screw thread 4 and the length of the tapered male screw thread 18 are determined in accordance with Japanese Industrial Standards, it is difficult to make the pipe joint smaller in scale. In addition, when a sealing tape or sealing material is used, upon threading (screw rotation) thereof, fragments or debris of the sealing tape or the sealing material become intermixed inside the fluid flow passage, and as a result, such powders are introduced from the end cap 2 into the cylinder chamber, leading to a concern that operations of the cylinder itself will be obstructed.
Still further, when the sealing tape or the sealing material has been used once and the pipe joint 6 is taken out from the end cap 2, the sealing tape or the sealing material cannot easily be reused. Thus, when the pipe joint 6 is reinstalled with respect to the end cap 2, a need arises for a sealing tape or a sealing material to be newly prepared, which is troublesome.